GIS Lecture 9a Notes PDF

Raster Operators for Analysis: Local Functions The Raster Data Model represents continuous data using grid cells, contrasting with the object-based Vector Data Model. Raster analysis focuses on different tools and operations, categorized into four main function types: local, focal, zonal, and globa...

Raster Operators for Analysis: Local Functions The Raster Data Model represents continuous data using grid cells, contrasting with the object-based Vector Data Model. Raster analysis focuses on different tools and operations, categorized into four main function types: local, focal, zonal, and global. This lecture focuses on local functions, which analyze data on a cell-by-cell basis. Categories of Local Functions 1.​ Reclassification ○​ Binary Masking: Assigns values (0 or 1) to represent absence/presence or suitability. Often an intermediate analysis step. ○​ Classification Reduction: Consolidates multiple attribute types into fewer classes, e.g., merging coniferous and deciduous forests into "forest." ○​ Classification Ranking: Assigns ranks or weights for further analysis, such as in least-cost path analysis. 2.​ Arithmetic Operations ○​ Include addition, subtraction, multiplication, and division applied to corresponding cells across layers. ○​ Example: Converting elevation data from feet to meters by multiplying by 0.305. 3.​ Logical Statements ○​ Boolean AND: Both conditions must be true for a value of 1; otherwise, the output is 0. ○​ Boolean OR: If either condition is true, the value is 1. ○​ Logical queries and map algebra can be performed using raster calculators. 4.​ Proximity Analysis ○​ Euclidean Distance: Calculates the straight-line distance of each cell to the nearest source cell. Useful as an intermediate step for analyses like buffering. Key Takeaways ​ Raster and vector operations are inherently different due to the data models. ​ Local functions focus on individual cells or corresponding cells across layers. ​ The local level serves as a foundation for advanced raster analyses involving focal, zonal, and global operations. Next, we'll explore focal functions, which include neighborhoods or windows surrounding cells.